Nathaniel B. Palmer 92-2
the proximity of the Antarctic Peninsula, the South Shetland Islands and the South Orkney Islands, allowing a much more gradual transition from the deep pack-ice to the open ocean boundary. We wish to thank Brett Castillo, Robert Swayzer, Preston Sullivan, Peter Amati, and John Cavanaugh for recording hourly ice observations. Thanks are also extended to Herb Baker for making and mounting the ice calibration stick over the side of the ship, and to the captain and crew of the Nathaniel B. Palmer for their support. Thanks to everybody's cooperation, the most complete set of ice observations were taken. This work was supported by National Science Foundation grant DPP 90-24809.
Snow properties and surfaceelevation profiles in the western Weddell Sea, (Nathaniel B. Palmer 92-2) V. I. LYTLE AND
S. F. ACKLEY
Dartmouth College and USA CRREL Hanover, New Hampshire 03755
During the Weddell Sea Cruise of the Nathaniel B. Palmer in May and June 1992, we occupied 15 ice stations, the location of which are shown in Ackley and Gow et al. 1992. At most of these stations ice cores were collected, surface snow and ice elevation lines were measured, and snow characterization was performed. The core collection and initial results are described in Gow et al. 1992; here we describe the snow pit measurements and the surface elevation surveys. These data will be used to estimate the heat flux to the atmosphere and salt flux to the ocean on the basis of snow and ice properties, and also provide surface properties to help in the interpretation of microwave satellite remote-sensng data. Thermodynamic ice-growth rate is determined by the heat .lux from the ocean to the atmosphere, which is in turn regulated y the thickness and properties of the ice and snow cover. The now cover can provide an insulating layer, significantly reducg the heat flux and slowing down the ice-growth rate. Particularly in the Weddell Sea it has been found, however, that the eight of the snow often depresses the ice surface below sea level Ackley et al. 1990; Lytle et al. 1990; Lange etal. 1990), resulting in an influx of sea water above the ice surface. As the sea water infiltrates the snow pack, a slush layer is created at the snow/ice terface. As this layer refreezes it will add to the ice thickness as ell as acting as a vapor and heat source to modify the snow cover. Significant algal growth can also occur in this layer (Sullivan et al. 1992). With the influx of this sea water, the ice
992 REVIEW
References Ackley, S. F., V. Lytle, B. Elder, and D. Bell. 1992. Sea-ice investigations on Ice Station Weddell #1: I. Ice Dynamics. Antarctic Journal of the U. S., this issue. Ackley, S. F. and V. I. Lytle. 1992. Sea-ice investigations on Ice Station Weddell #1: II. Ice thermodynamics. Antarctic Journal of the U.S., this issue. Ackley, S. F., A. J. Cow, V. I. Lytle, M. N. Darling, and N. E. Yankielun. 1992. Sea-ice investigations on Nathaniel B. Palmer: Cruise 92-2. Antarctic Journal of the U.S., this issue. Ackley, S. F., S. J . Smith, and D. B. Clarke. 1982. Observations of pack ice properties in the Weddell Sea. Antarctic Journal of the U.S., 17(5): 104-106. Allison, I. 1989. The East Antarctic Sea Ice Zone: Ice characteristics and drift. GeoJournal, 18, 103-115.
becomes isothermal, and continued ice formation occurs above the surface of the ice as this slush layer freezes, rather than at the bottom of the ice sheet. This ice formation process will result in a more rapid heat transfer rate to the atmosphere and possibly a different salt flux to the ocean than would the growth of congelation ice formed by continued ice growth at the bottom of the ice sheet. This slush layer has been found repeatedly in the Weddell Sea ice cover (Ackley and Lytle 1992; Ackley et al. 1990) and the subsequent refreezing of this slush has been estimated to affect as much as 50 percent or more of the total ice area in the western Weddell Sea. During this cruise, temperature, density, and grain size measurements were taken in the snow pack to estimate the heat flux through the ice and overlying snow. In addition, elevation measurements were collected to estimate the amount of ice which was above or depressed below sea level and snow and ice properties were collected to estimate the amount of ice which had been formed due to the refreezing of this slush layer. These measurements in conjunction with the ice core program in the same area (Gow et al. 1992), will be used to describe whether this process of the freezing of the slush had also occurred earlier, and to estimate the cumulative associated heat and salt flux. Two snow pits were dug and analyzed at each station, one near where the cores were extracted and a second where the radar data were collected (Yankielun and Ackley 1992). Figure 1 is an example of the data collected from a snow pit on site number 5. Note the large grain sizes near the base of the snow pit, indicating that a significant amount of metamorphism has occurred. This is most likely being influenced by the infiltration of brine, as supported by the salinity (5 ppt) in the bottom layer of the snow. Additional snow pits were analyzed at four of the stations, where there were significant variations in snow or ice thickness across the floe. Snow temperatures, densities, dielectric properties, grain sizes, and salinities were measured as a function of depth in the snow pack. In addition, snow and ice samples were collected for stable isotope analysis which will help estimate the relative amount of snow which had been incorporated in the sea ice. Snow depths for the pits varied from 10 centimeters to 85 centimeters, with snow salinities varying from 0 ppt up to as much as 63 ppt. We found significant variability in the pits both between sites and at the same sites. The presence of layers in the snow
93
70 60 so
40 30
10 0 -10
0 20 40 60 80 100
Length Along Surface (m)
Figure 1. Snow pit profile from site number 5. The snow grain size, density, and temperature for each layer are indicated.
Snow Surface -31.8
42 39
a
I
28
References
-25.0
SN
a
rA
V
13 10
-20.1
0
-13.5 ice surface
Figure 2. Example of surface profile data. Ice and snow surface elevations were measured every 0.5 meters over a 100-meter line.
94
resulted in order of magnitude variations in snow grain size (
Snow properties and surfaceelevation profiles in the western Weddell Sea, (Nathaniel B. Palmer 92-2) V. I. LYTLE AND
S. F. ACKLEY
Dartmouth College and USA CRREL Hanover, New Hampshire 03755
During the Weddell Sea Cruise of the Nathaniel B. Palmer in May and June 1992, we occupied 15 ice stations, the location of which are shown in Ackley and Gow et al. 1992. At most of these stations ice cores were collected, surface snow and ice elevation lines were measured, and snow characterization was performed. The core collection and initial results are described in Gow et al. 1992; here we describe the snow pit measurements and the surface elevation surveys. These data will be used to estimate the heat flux to the atmosphere and salt flux to the ocean on the basis of snow and ice properties, and also provide surface properties to help in the interpretation of microwave satellite remote-sensng data. Thermodynamic ice-growth rate is determined by the heat .lux from the ocean to the atmosphere, which is in turn regulated y the thickness and properties of the ice and snow cover. The now cover can provide an insulating layer, significantly reducg the heat flux and slowing down the ice-growth rate. Particularly in the Weddell Sea it has been found, however, that the eight of the snow often depresses the ice surface below sea level Ackley et al. 1990; Lytle et al. 1990; Lange etal. 1990), resulting in an influx of sea water above the ice surface. As the sea water infiltrates the snow pack, a slush layer is created at the snow/ice terface. As this layer refreezes it will add to the ice thickness as ell as acting as a vapor and heat source to modify the snow cover. Significant algal growth can also occur in this layer (Sullivan et al. 1992). With the influx of this sea water, the ice
992 REVIEW
References Ackley, S. F., V. Lytle, B. Elder, and D. Bell. 1992. Sea-ice investigations on Ice Station Weddell #1: I. Ice Dynamics. Antarctic Journal of the U. S., this issue. Ackley, S. F. and V. I. Lytle. 1992. Sea-ice investigations on Ice Station Weddell #1: II. Ice thermodynamics. Antarctic Journal of the U.S., this issue. Ackley, S. F., A. J. Cow, V. I. Lytle, M. N. Darling, and N. E. Yankielun. 1992. Sea-ice investigations on Nathaniel B. Palmer: Cruise 92-2. Antarctic Journal of the U.S., this issue. Ackley, S. F., S. J . Smith, and D. B. Clarke. 1982. Observations of pack ice properties in the Weddell Sea. Antarctic Journal of the U.S., 17(5): 104-106. Allison, I. 1989. The East Antarctic Sea Ice Zone: Ice characteristics and drift. GeoJournal, 18, 103-115.
becomes isothermal, and continued ice formation occurs above the surface of the ice as this slush layer freezes, rather than at the bottom of the ice sheet. This ice formation process will result in a more rapid heat transfer rate to the atmosphere and possibly a different salt flux to the ocean than would the growth of congelation ice formed by continued ice growth at the bottom of the ice sheet. This slush layer has been found repeatedly in the Weddell Sea ice cover (Ackley and Lytle 1992; Ackley et al. 1990) and the subsequent refreezing of this slush has been estimated to affect as much as 50 percent or more of the total ice area in the western Weddell Sea. During this cruise, temperature, density, and grain size measurements were taken in the snow pack to estimate the heat flux through the ice and overlying snow. In addition, elevation measurements were collected to estimate the amount of ice which was above or depressed below sea level and snow and ice properties were collected to estimate the amount of ice which had been formed due to the refreezing of this slush layer. These measurements in conjunction with the ice core program in the same area (Gow et al. 1992), will be used to describe whether this process of the freezing of the slush had also occurred earlier, and to estimate the cumulative associated heat and salt flux. Two snow pits were dug and analyzed at each station, one near where the cores were extracted and a second where the radar data were collected (Yankielun and Ackley 1992). Figure 1 is an example of the data collected from a snow pit on site number 5. Note the large grain sizes near the base of the snow pit, indicating that a significant amount of metamorphism has occurred. This is most likely being influenced by the infiltration of brine, as supported by the salinity (5 ppt) in the bottom layer of the snow. Additional snow pits were analyzed at four of the stations, where there were significant variations in snow or ice thickness across the floe. Snow temperatures, densities, dielectric properties, grain sizes, and salinities were measured as a function of depth in the snow pack. In addition, snow and ice samples were collected for stable isotope analysis which will help estimate the relative amount of snow which had been incorporated in the sea ice. Snow depths for the pits varied from 10 centimeters to 85 centimeters, with snow salinities varying from 0 ppt up to as much as 63 ppt. We found significant variability in the pits both between sites and at the same sites. The presence of layers in the snow
93
70 60 so
40 30
10 0 -10
0 20 40 60 80 100
Length Along Surface (m)
Figure 1. Snow pit profile from site number 5. The snow grain size, density, and temperature for each layer are indicated.
Snow Surface -31.8
42 39
a
I
28
References
-25.0
SN
a
rA
V
13 10
-20.1
0
-13.5 ice surface
Figure 2. Example of surface profile data. Ice and snow surface elevations were measured every 0.5 meters over a 100-meter line.
94
resulted in order of magnitude variations in snow grain size (
